Make the expr syntax explicit in the docs

doc/ledger3.texi

@@ -8252,34 +8252,34 @@ The amount can be any kind of amount supported by ledger,
 with or without a commodity.  Use this for decimal values.
 
 @item /REGEX/
-@itemx expr account =~ /REGEX/
+@itemx expr "account =~ /REGEX/"
 A regular expression that matches against an account's full name.  If
 a posting, this will match against the account affected by the
 posting.
 
 @item @@/REGEX/
-@itemx expr payee =~ /REGEX/
+@itemx expr "payee =~ /REGEX/"
 A regular expression that matches against a transaction's payee name.
 
 @item %/REGEX/
-@itemx expr has_tag(/REGEX/)
-@itemx expr has_tag('TAG')
+@itemx expr "has_tag(/REGEX/)"
+@itemx expr "has_tag('TAG')"
 A regular expression (REGEX) or string (TAG) that checks for the tags of
 a transaction.
 
-@item expr has_meta(/REGEX/)
-@itemx expr has_meta('TAG')
+@item expr "has_meta(/REGEX/)"
+@itemx expr "has_meta('TAG')"
 A regular expression (REGEX) or string (TAG) that checks for the metadata
 key of a transaction.
 
-@item expr tag(REGEX) =~ /REGEX/
+@item expr "tag(REGEX) =~ /REGEX/"
 A regular expression that matches a transaction's tags against its values.
 
-@item expr date =~ /REGEX/
+@item expr "date =~ /REGEX/"
 Useful for specifying a date in plain terms.  For example, you could say
-@samp{expr date =~ /2014/}.
+@samp{expr "date =~ /2014/"}.
 
-@item expr comment =~ /REGEX/
+@item expr "comment =~ /REGEX/"
 A regular expression that matches against a posting's comment
 field.  This searches only a posting's field, not the transaction's note
 or comment field.  For example, @code{ledger reg "expr" "comment =~
@@ -8303,7 +8303,7 @@ but will not match:
 To match the latter, use @samp{ledger reg "expr" "note =~ /landline/"}
 instead.
 
-@item expr note =~ /REGEX/
+@item expr "note =~ /REGEX/"
 A regular expression that matches against a transaction's note field.
 This searches all comments in the transaction, including comments on
 individual postings.  Thus, @samp{ledger reg "expr" "note =~ /landline/"}
@@ -8333,23 +8333,23 @@ A sub-expression is nested in parenthesis.  This can be useful passing
 more complicated arguments to functions, or for overriding the natural
 precedence order of operators.
 
-@item expr base =~ /REGEX/
+@item expr "base =~ /REGEX/"
 A regular expression that matches against an account's base name.  If
 a posting, this will match against the account affected by the
 posting.
 
-@item expr code =~ /REGEX/
+@item expr "code =~ /REGEX/"
 A regular expression that matches against the transaction code (the
 text that occurs between parentheses before the payee).
 
-@item expr any(KEYWORD =~ /REGEX/)
+@item expr "any(KEYWORD =~ /REGEX/)"
 The @command{any} keyword is used to specify that at least one posting of
 the transaction must match the expression in brackets.  For example,
 @samp{ledger -f d reg expr "any(account =~ /Assets:/)"} can be used to
 display all transactions which involve at least one @samp{Assets:}
 account.
 
-@item expr all(KEYWORD =~ /REGEX/)
+@item expr "all(KEYWORD =~ /REGEX/)"
 The @command{all} keyword is used to specify that all postings of a
 transactions must match the expression in brackets.  For example,
 @samp{ledger -f d reg expr "all(account =~ /Assets:/)"} can be used to